Explain the Kidney as an Endocrine Gland

The kidney produces substances that can be described as hormones. Hormones are the chemicals produced by glands in the body and circulate in the bloodstream. Etythropoietin, a glycoprotein, IS released from the kidneys in response to the tissue hypoxia. It stimulates the production of red blood cells by the bone marrow. The cellular site of production of erythropoietin is not clearly known, but acts as a hormone. 'The liver converts vitamin D (cholecalciferol) to 25-hydroxycholecalciferol. This 25- hydroxy compound is then converted into 1, 25-dihydroxycholecalciferol by the kidney when the plasma calcium level is below normal. This di-hydroxy compound of vitamin D is much more active than the original vitamin in bringing about the absorption of calcium from the intestine and can be considered a hormone produced by the kidney.

An inadequate blood flow to the kidneys leds to the release of a protease enzyme called renin. Renin is secreted from juxtaglomerular apparatus (a group of cells located between afferent and efferent arterioles). It combines with angiotensinogen to form angiotensin I and angiotensin II, which is a powerful vasoconstrictor and increases the blood pressure. It also stimulates aldosterone (mineralocorticoid) secretion of the adrenal cortex.